public class MutablePoint {
    private volatile int x, y;

    public MutablePoint(int x, int y) {
	this.x = x;
	this.y = y;
    }

    public synchronized void setX(int v) { x = v; }
    public synchronized void setY(int v) { y = v; }

    public int getX() { return x; } // no sync OK since x is volatile
    public int getY() { return y; } // no sync OK since y is volatile

    // This method is complicated because we have to make sure that
    // the X and Y values we compare are consistent---that a mutation
    // does not occur after retrieving one integer but before
    // retrieving the other
    public boolean equals(Object o) {
	if (o instanceof MutablePoint) {
	    MutablePoint p = (MutablePoint)o;
	    int px, py;
	    synchronized (p) {
		px = p.getX();
		py = p.getY();
	    }
	    synchronized (this) {
		return (px == getX() && py == getY());
	    }
	}
	return false;
    }
}